A power delivery system receives power from a source connected to its input terminals and delivers current to a load connected across its output terminals. Examples of power delivery systems include voltage regulators, such as switching DC/DC converters, linear regulators, and load switches.
It is often desired that protection features be implemented in the power delivery system to improve system performance and reliability. One such feature is the current limiting function of the power delivery system. Current limiting function limits the load current to a predetermined safe level under potential overload fault conditions, such as when the output is short circuited to the ground. During normal operations, when the required load current is below the current limit level, the current limiting function does not affect the operation of the power delivery system.
The characteristics of certain loads may exhibit temporary high current requirements beyond the nominal current limit, even during a normal operation. For example, inertial loads, such as electric motors, usually require a higher current during the spin-up phase than the steady-state phase. To supply loads when there is a surge in their current requirements, it is desirable that the power delivery system temporarily increase its output current to a level above the nominal current limit. Disabling the current limit function temporarily to allow for current surges is unsafe as it would leave the power delivery system unprotected and expose it to potentially destructive conditions.
FIG. 1 shows a conventional power control block 100 of a power delivery system delivering current to a load 150. Power control block 100 receives power via its input terminal IN, and in response, delivers power to load 150 via its output terminal OUT. The power delivery system (not shown) may be a voltage regulator, such as a switching DC/DC converter, a linear regulator or it can be a power switch. Power control block 100 includes a current limiting function which limits the output current IOUT to a level defined by reference signal CLIMREF applied to input terminal CLIMREF of power delivery system 100.
In order to successfully handle current surges, the current limit reference signal CLIMREF must be selected such that the resulting current limit level is higher than the expected current surge required by load 150. Since the relatively high current limit defined by CLIMREF is active even after the surge dissipates, power delivery system 100 and its input supply are exposed to higher than nominal current levels under overload fault conditions, such as when the output is shorted to ground. A need continues to exist for a power delivery system that does not suffer from the disadvantages of conventional power delivery systems and is protected during overload fault conditions at all times even when there is a surge in the required current level.